Alan Kay has had about a few decades to empirically demonstrate that "we" have willfully made it complicated. I don't believe he has done so.
Have you used OMeta? That came out ouf VPRI I believe: https://en.wikipedia.org/wiki/OMeta . It is a really nice approach to constructing parsers and interpreters. Then there is "Open, extensible object models": https://www.recurse.com/blog/65-paper-of-the-week-open-exten... . Again by the same folks. Those are the one that come to mind when I think of simple and very powerful tools. There are many others. So I think…
But what has been built with these tools? If OMeta was really better, wouldn't we be using it to parse languages by now? They already have a successor Ohm, which is interesting, but I also think it falls short.
I'm searching desperately for a meta-language to describe my language, so I would use it if it were better.
I think they generally do the first 90%... but skip out on the remaining 90% (sic) you need to make something more generally useful and usable.